1. Field of Invention
The invention relates to making a multiple actuator device insensitive to thermally-induced expansions and contractions.
2. Description of Related Art
In existing thermal ink jet printing devices, the printhead cartridge comprises one or more ink-filled printheads. In a common design for an ink jet printer, the cartridge is mounted upon a movable carriage. The printheads of the object printer are arranged opposite a sheet of recording medium on which an image is to be printed. During printing, the cartridge is moved with the carriage across the sheet in repeatable swaths to form an image, much like a typewriter. During non-printing, the cartridge is at rest awaiting instructions from, for instance, an electronic controller. In another common ink jet printer design, the cartridge is stationary and the paper is moved across an array of printhead nozzles that span the full-width of the cartridge. In yet another multi-head device, for example, a charged coupled device (CCD) array having a plurality of sensor heads, the sensor heads receive varying color and image information for subsequent reproduction on a recording medium.
Mounting the sensor or print-heads on the carriage of a multi-head device requires the multi-heads to be initially spaced apart a designated, or nominal, distance relative to the other respective heads. Thus, when the temperature of the carriage on which all of the printheads, or sensor heads, are mounted changes, the carriage undergoes thermal expansion or contraction. Whenever the temperature of the carriage changes from a nominal temperature, at which the heads are at the nominal spacing, the thermal expansion or contraction of the carriage will cause the actual spacing between the printheads, or sensor heads, to differ from the nominal spacing. As a result, ink droplets are deposited on the recording medium at improper locations in the case of a multi-head printer. Similarly, image data is received at improper locations in the case of, for example, a CCD sensor array. Thus, the thermally-induced movement of the printheads or sensor heads tends to cause a mis-registration of colors or print images, or of sensed color separation layers, of due to improper, or at least inconsistent, positioning of the printheads or sensor heads relative to one another.
Precision placement of ink droplets, or the precision reception of image data, is essential to lessen contaminating color shifts, or blurring or shifting of colors that otherwise occur due to thermal expansion of the carriage the plurality of printheads, or sensor heads, are mounted upon. The correct droplet, or pixel, alignment becomes increasingly important in high-end printing, such as photographic printing or acoustic inkjet printing, in which very small droplets of ink are used.
This invention provides apparatus that are insensitive to thermally-induced spacing variations between multiple actuators, such as printheads or sensor heads, in a multi-actuator device. This invention separately provides methods and apparatus that increase the efficiency of image generating multi-actuator devices. This invention also separately provides methods and apparatus resulting in precision placement of image producing materials for accurate image reproductions and increased color clarity.
The methods and apparatus of the invention are derived, in part, from an 18th century application for controlling pendular motions in clocks. In the pendular motion controlling technique, materials having different thermal expansion properties carefully controlled the effective swing length of a clock""s pendular arm. By using materials of known thermal expansion properties, the time period of the pendular swing was consistently controlled relative to gears within the clock casing housing the pendular arm and the clock""s gears. The technique permitted the precision necessary for proper and consistently reliable time-keeping notwithstanding the changing thermal conditions the clock was subjected to. In the systems and methods according to this invention, that concept is applied to control spacing in multi-actuator devices.
Further, while previous printers required manual correction of the multiple printheads of an image producing device to achieve proper alignment of the multiple printheads relative to one another, the methods and apparatus according to this invention reduces the need for manual correction, decreasing the occurrence of human error and increasing the precision placement of ink droplets, or the precision reception of image data. As a result, multiple actuator imaging devices are easier to operate and become more effective.
In various exemplary embodiments of the invention, the spacing between multiple actuators, such as printheads or sensor heads, is controlled or rendered insensitive to thermally-induced expansion or contraction by fixing a first actuator to an underlying common carriage or frame. All of the other actuators are linked to the first actuator by links of two dissimilar materials having different coefficients of thermal expansion. In particular, the other actuators are not fixed to the carriage or frame. Instead, the other actuators are xe2x80x9ccantileveredxe2x80x9d off, i.e., fixed to, the first actuator by the link and are merely supported by the carriage or frame. In other words, the other actuators xe2x80x9cfloatxe2x80x9d relative to the carriage or frame. As a result, when the underlying carriage or frame undergoes thermal expansion or contraction, the distance between the linked actuators remains constant. This tends to reduce, if not eliminate, thermally-induced spacing shifts between the actuators. In a printer having printheads as the actuators, this also tends to improve the placement of the ink droplets ejected from each printhead onto the recording medium. In a scanner having multiple CCD array sensor heads as the actuators, the reception of image data by a sensor head for subsequent reproduction onto a recording medium is improved. In CCD array sensor heads, for example, the reduction of thermally-induced spacing shifts tends to reduce mis-registration between the various color separations.
Thus, the apparatus and methods according to this invention reduce the need for an operator to manually correct the spacing between actuators due to thermally-induced spacing shifts. Further, the apparatus and methods according to this invention enable the proper ink droplet placement onto a recording medium in a multiple printhead ink jet printer to be maintained. The apparatus and methods according to this invention make a multiple actuator image forming or printing process easier and more precise than previous multiple actuator image forming or printing devices.
These and other features and advantages of this invention are described in, or are apparent from, the following detailed description of various exemplary embodiments of the systems and methods according to this invention.